Tourists visit this region for one thing--the wildlife park. It's well worth the journey since you can see the widest variety of wildlife in Nepal.
I recommend the jeep safari as part of your package; your best chances for seeing more wildlife will come from this experience. You cover more ground and a wider variety of terrain--for example, we saw 7 rhinos during the same time other people taking an elephant ride saw just one rhino that was mostly obscured. Besides, many parks worldwide are shutting down elephant rides for wildlife concerns. Chitwan will continue these rides as long as there is a tourist demand (it is declining a bit currently).
The rarest animal we saw during the jeep safari was a sloth bear. Although we didn't see tigers or leopards, we did see their footprints during a walking safari. We also saw a number of crocodiles and a gavial during a 45 minute canoe ride.
Another highlight to experience at Chitwan is a local Taru cultural music and dance show. This is one way tourists can actively preserve this unique and valuable Nepali culture.More